Schizophrenia affects approximately 24 million people worldwide. This disorder, however, is treatable, and treatment at the initial stage thereof is effective. Nonetheless, more than 50% of people with schizophrenia have not undergone appropriate treatment.
Examples of currently commercially available therapeutic agents for schizophrenia include chlorpromazine, haloperidol, clozapine, risperidone, olanzapine, quetiapine, ziprasidone, aripiprazole, amisulpride, and paliperidone.
It is known that positive symptoms, negative symptoms, and/or cognitive impairment of schizophrenia can be improved by inhibition of PDE10A, and it is further known that schizophrenia can also be treated by inhibition of PDE10A (e.g., Patent Literatures 1 to 15 and Non-patent Literatures 1, 3 to 5, and 9 to 12).
In addition, studies have also been made on PDE10A knockout mice (e.g., Non-patent Literature 7) and the treatment of Huntington's disease, mental illness, or the like by inhibition of PDE10A (e.g., Non-patent Literatures 2, 6, and 8).